Comments on: Why Windows Vista only sees 3GB memory in a PC with 4GB RAM and how Vista SP1 fools its users

By: Michael Pietroforte

Michael Pietroforte — Sat, 21 Mar 2009 17:31:49 +0000

Does the BIOs see 4GB RAM? Perhaps one of your modules is defect.

By: Carlos

Carlos — Wed, 18 Mar 2009 00:14:11 +0000

I think this post is kinda old, but I am running Windows 7 Beta 64bit and I am only seeing 3gb of ram used. It does say that I have 4, but I tried to run virtual PC and it said I did not have enough. I have 4gb. System was using 2gb and vm was set for 1gb????????????

I am updating my bios right now, but I will repost if thatfixes it. I think that would do it. I can see how all these factors, chipset, bios, OS, 32 vs 64 would have an impact on the amount of memory a system can address, but I do not think it is one single thing that does it.

By: leek

leek — Tue, 24 Feb 2009 18:20:27 +0000

Without going into BIOS or Windows issues (which others have addressed), I’d like to point out that:

- On some motherboards it may be better to use 4 GB instead of 2 GB or 3 GB because of memory interleaving improving performance. I have a SuperMicro MB that supports 4 1 GB DDR2 modules, and prefers them in pairs for interleaving. So even if I don’t use 4 GB, I get improved performance by installing DIMMs in pairs.

By: Sri

Sri — Mon, 22 Dec 2008 17:41:10 +0000

Hi Guys,

I’m also having the same problem. I installed 4GB, It is perfectly showingin BIOS. But When it comes to Vista, it is using only 3GB. I’m using 32bit OS.
Any suggestion is appreciated..

thanks.

By: 32bit sau 64bit | Clocky's Blog

32bit sau 64bit | Clocky's Blog — Sun, 14 Dec 2008 17:57:33 +0000

[...] nu stia sa foloseasca decat 3,2 GB din cei 4 GB pe care ii aveam desi cu SP1 Microsoft incerca sa musamalizeze chestiunea. Asa ca am decis sa incerc si eu marea cu degetul.E de notat ca daca ai o versiune [...]

By: Vista fools users with SP1 - Operating Systems - TechEnclave

Vista fools users with SP1 - Operating Systems - TechEnclave — Sun, 21 Sep 2008 05:37:47 +0000

[...] permalink Vista 32bit conveniently fools users by displaying that it can use 4GB of installed RAM in the system properties, whereas it cant use use more than 3GB to find it out, go to msinfo32 Total physical memory is the one OS actually uses see for urself My computer –> Properties Msinfo32 Source: 4sysops – Why Windows Vista only sees 3GB memory in a PC with 4GB RAM and how Vista SP1 fools its us… [...]

By: Akshay

Akshay — Sat, 23 Aug 2008 23:49:48 +0000

Hi guys..
i m using windows vista 64 bit service pack 1 . i installed 4 gb of ram but its showing same as 3.12gb . So its not the matter of 32 bit or 64 bit , moreover service pack 1 didnt able to slove this problem. So if u guys a have any idea pls post or mail me at aks7sach@rediffmail.com

By: Severn

Severn — Thu, 14 Aug 2008 19:29:08 +0000

err. anyone heard of windows 2000?

the server version (32bit thankyou very much) had a little thing called 36bit memory addressing. voila!!! we have 128GB of ram to play with

now, microsoft; get coding and give me more than 3.5GB ram, or give me decent support for X64 windows xp/vista.

By: Andrew

Andrew — Mon, 11 Aug 2008 05:29:47 +0000

I am just on the verge of buying a new laptop with Vista Business pre-installed.
I WAS thinking of upgrading the standard 2GB memory to 4GB, but I now know that would be a waste of money.
But…
If I only upgrade to 3GB, would Vista then set aside a GB of that, leaving me with just over 2GB usable?
If that were the case, perhaps I would be better off buying 4Gb – 1 for Vista and 3 for me.

By: Alex Sheppard-Godwin

Alex Sheppard-Godwin — Wed, 06 Aug 2008 12:30:54 +0000

When Vista 32bit or any other 32bit OS does support 4GB or more of RAM it will undoubtedly result in a drop in performance.
METAPHORE
Most of my metaphores serve to confuse so here you go – get confused – It’s like owning a Pool table in an apartment that is big enough for a pool table. Then adding a loft extension and suggesting you can now own a snooker table. Indeed if you chop the snooker table in half and put half of it in the loft you can have it or you could fill the room with it and leave no space to wander round and take your shot. However its not so hard to stick a cushion down the cut edges and make two smaller tables. Now you can use your snooker table for two games of pool.
IN THE MACHINE
The fact is a 32bit OS can only access 4 GB of memory space. Included in this space is everything. When you read some data from the disc it gets stored in a space with an address – that address is in the list of 4billion available addresses. The same thing is true if you have a 512mb graphics card 512million of those addresses must be taken out of your RAM addresses and reserved just to get data onto the screen. Every time you press a key on your keyboard, receive some data over the network, send an image over USB to your printer or make a sound that information is transferred to and from the devices via those addressed locations. The Chipset is responsible for organising this mapping. It maps the physical addresses into a virtual 4GB space.
TOO CLEVER TO TRY
It could try and be clever and say when I want to display stuff on the screen map it to the graphics card and when I want my app to use it map it to my RAM chips. If the app that is in that RAM area wants to write to the screen you can see life will become very tricky and the whole process to continue the metaphor would involve running up the stairs and launching the balls at the same velocity on the other half of the table.
DUAL CHANNEL PAYBACK
However there is an upside – you probably haven’t wasted you cache on that extra memory. The reason for this is that if you install pairs e.g. 2×2gb of the same type the system can access both pairs simultaneously double the speed memory can be accessed. If you got to 4 GB with 1 x 2 GB and 1 x 1 GB then you probably won’t see in improvement and dual channel memory access can’t be enabled across that 1 x 2 GB chip. The PTA switches try to map the 32bit code in a 36bit address space because it’s really 64bit hardware.
VMWARE ALL YOUR MEMORY IN BITE SIZES
A last resort could involve running something like 64bot Linux with 64bit VMware host. This will allow multiple 32bit Virtual machines and get you all of your memory. Of course at a cost of multiple OS’s running and hardware abstraction that means you won’t get the best out of your cool kit.
THE EXCEPTION TO PROVE THE RULE
Lastly more advanced versions of applications like SQL server are written to optimised use of those 32/36 bit memory extensions. But there are very few applications that have gone to the effort to make that work.
DISCLAIMER
I have written this based on my very fuzzy memory but I think it describes why you should stop waiting for a 32bit OS to use all 4 GB or more of your RAM. If you want to find out more you should look at how Virtual Memory works, and How page faults trigger memory management and what Context switching means.

By: Bryan

Bryan — Sun, 27 Jul 2008 18:46:56 +0000

Mark Russinovich has put together some interesting information on the issue:

http://blogs.technet.com/markrussinovich/archive/2008/07/21/3092070.aspx

By: Kihwan Kim

Kihwan Kim — Thu, 29 May 2008 15:46:35 +0000

Thanks for useful information. It helped me alot!

By: Oh Windows why do you only support 4GBs!!WHY!! «

Oh Windows why do you only support 4GBs!!WHY!! « — Wed, 28 May 2008 01:05:07 +0000

[...] http://4sysops.com/archives/why-windows-vista-only-sees-3gb-memory-in-a-pc-with-4gb-ram-and-how-vist... [...]

By: Ryan H

Ryan H — Tue, 20 May 2008 12:59:43 +0000

PAE (Physical Address Extension) is a hack Intel came up with to address the increasing memory needs of customers using their platforms until they could push their first (debatably failed) 64-bit platform out (i.e Itanium). PAE extends the the address space form 32-bits to 36-bits at the expense of system performance.

The problem is drivers that aren’t specifically programmed to be aware of PAE can become unstable if an address they need happens to be paged out to an address in the extra 4-bits of address space. MS decided in XP SP2 that PAE would be handicapped to get around these stability issues (it still has to be on for hardware DEP to function the kernel just doesn’t allow programs to access the extra space) because of the driver stability problems. Don’t blame MS for this problem, blame the sloppy driver developers.

By: Michael

Michael — Tue, 13 May 2008 19:45:08 +0000

Alex, it seems you have a hardware problem. Maybe some of your memory modules are broken or your motherboard can’t use them. I would remove the modules one by one to figure out which of them work. You should also enable memory remapping in the BIOS.

By: alex

alex — Sun, 11 May 2008 16:18:43 +0000

I have Vista Ultimate x64 and SP1 but my computer still says i have exactly 3gb of physical RAM installed while i actually have 6gb (1gbx2 2gbx2) installed in the four slots on my motherboard what should i do?

By: Gskill DDR2 6300 + Crucial DRR2 4200 - Overclock.net - Overclocking.net

Gskill DDR2 6300 + Crucial DRR2 4200 - Overclock.net - Overclocking.net — Thu, 24 Apr 2008 23:44:41 +0000

[...] memory that now "fills the hole". Here’s two articles that might help you understand: Article 1 Article 2 There’s really not many situations that would result in more than 3GB of memory being [...]

By: Michael

Michael — Mon, 21 Apr 2008 18:39:57 +0000

David, what is the name of the manufacturer of your board? Sending them an email might indeed be helpful. The more complaints they get the earlier they will offer a BIOS update that supports memory remapping.

Ryan, thanks for the link. That’s really a comprehensive article about this topic.

By: David

David — Sat, 19 Apr 2008 02:50:11 +0000

Indeed I have and while my chipset supports memory remapping in theory, as it is new (P35) in reality the company whom made the board did think to include it as a bios option (lastest bios). Therefore I am stuck and have given up.
Maybe I will just send a nasty email to board manufacturer!
So while this is annoying, 4GB or not I will stick with Vista 64 which (this may be controversal) on my system at least, benchmarked against xpsp2/32, is now up to 70% faster in some areas.
To finish, Im in on the side of its all Motherboard critical, once that issues sorted the rest is mathmatical, i.e. follow OS guidelines, 32bitOS you not getting 4GB unless its a special one and your investing time to play with it.

By: Ryan

Ryan — Fri, 18 Apr 2008 22:53:57 +0000

Here’s the article I was referring to, in case anyone is interested. It’s a year old so I’m hoping memory hole remapping has become more stable than he implies: http://www.dansdata.com/askdan00015.htm